For example, in a wastewater produced in a process of purifying exhaust gas discharged from a coal gasification furnace, so-called COD (Chemical Oxygen Demand) components, such as organic materials, are contained. It has been difficult to remove the COD components by a coagulation sedimentation process, which involves a step of adding any of coagulants, such as iron chloride and PAC.
An oxidation treatment with any of oxidizing reagents, such as sodium hypochlorite (NaClO) and hydrogen peroxide can not achieve high efficiency, limiting a removal rate of a COD component to as a low level as approximately 60%.
Even if a treatment with ozone, a further strong oxidizing reagent, is applied, the removal rate is at the level of 80%, and thereby, this treatment also can not satisfy a given effluent standard if a COD concentration is high. Furthermore, it is exceptionally difficult for activated carbon to absorb this type of COD components, resulting in consumption of a large amount of activated carbon to satisfactorily treat the COD components.
In order to treat COD containing wastewater contained in such a refractory coal gasification wastewater, it has been proposed that the COD components are contacted with weakly or moderately basic anion exchange resin so as to absorb the COD components to the anion exchange resin (Patent Document 1).
Patent Document 1: Japanese Patent Application Laid-Open No. 2003-305467